El device

ABSTRACT

The present invention relates to an EL device which is driven with a lower voltage or power amount, which is superior in interface stability between layers in the device and which has a higher luminance as compared with the use of a conventional electrode, and is characterized in that in the EL device comprising a light emitting layer disposed as an essential layer between two electrodes facing each other, at least one of the electrodes includes a crystalline conductive film whose diffraction intensity ratio of (400)/(222) is 1.0 or more in X-ray diffraction by a θ/2θ method.

TECHNICAL FIELD

The present invention relates to an electrode for use in an EL device,further particularly to an improvement of a hole injection electrodewhich supplies a hole (positive hole) to a light emitting layer using anorganic compound.

BACKGROUND ART

In recent years, considerable research has been done on an organic ELdevice. It has been noted that this is a device having a basicconstitution in which hole transport materials such as triphenyl diamine(TPD) are formed into a thin film on a hole injection electrode by vapordeposition, fluorescent materials such as alumiquinolinol complex (Alq3)are further stacked as a light emitting layer, and metal electrodes(electron injection electrode) having a small work function, such as Mg,are formed, and a remarkably high luminance of several 100 to several10,000 cd/m² is obtained at a voltage of around 10 V.

It is considered that materials for use as the hole injection electrodeof the organic EL device, which inject many holes into the lightemitting layer, hole injection/transport layer or the like, areeffective. In many cases, a constitution for usually taking an emittedlight from a substrate side is used, and a transparent conductivematerial is required.

As this transparent electrode, indium tin-doped oxide (ITO), indiumzinc-doped oxide (IZO), ZnO, SnO₂, In₂O₃ or the like is known. Aboveall, an ITO electrode is used as a transparent electrode having both avisible ray transmittance of 90% or more and a sheet resistance of 10Ω/□ or less, broadly used as the transparent electrode for a liquidcrystal display (LCD), light control glass, solar battery and the like,and regarded as promising also as the hole injection electrode for theorganic EL device.

Additionally, the organic EL device tends to be degraded with an elapseof time, and prevention of degradation of the device is an importantproblem. Various causes are considered as factors which degrade thedevice, but the degradation of a film interface between an electrode andan organic layer largely influences device life or emissioncharacteristics, and it is an important problem to modify physicalproperties in the film interface. Moreover, a generation/enlargementphenomenon or the like of a non-emission region, referred to as anabnormal emission phenomenon or dark spot by a leak current, also needsto be prevented.

As an improvement of the electrode, in Japanese Patent ApplicationLaid-Open No. 11-87068, it has been described that an ITO electrodehaving a (111) orientation and preferably having a diffraction intensityratio of (400)/(222) of 0.6 or less in X-ray diffraction by a θ/2θprocess is used as the ITO electrode which is a hole injectionelectrode. Furthermore, it is described that an electrode having anaverage surface roughness of ITO electrodes of Ra≦10 nm and a maximumsurface roughness of Rmax≦50 nm is preferably used.

Moreover, in Japanese Patent Application Laid-Open No. 6-76950, anorganic EL device is described in which a light emitting layer formed ofan organic compound is disposed as an essential layer between twoelectrodes facing each other, an electron injection/transport layerformed of an organic compound is disposed if desired, and at least oneof two electrodes is a transparent or translucent electrode. In theorganic EL device, a size of a micro crystal grain on the surface of thetransparent or translucent electrode, contacting the light emittinglayer or the electron injection/transport layer, is 500 angstroms orless. By the use of this electrode, luminance unevenness and emissionstability can be improved.

DISCLOSURE OF THE INVENTION

There has been a problem that the improvement of the electrode describedin any of the above-described publications is insufficient as animprovement for obtaining an EL device driven at a lower voltage to emita light with a high luminance. If the driving voltage is low andhigh-luminance emission is obtained, influences on an organic compoundin a light emitting layer, or an interface between the electrode and thelight emitting layer or a hole injection/transport layer can be reduced,and therefore it can be said that there is a possibility that even theproblems described in the above-described publications can be solved.

An object of the present invention is to provide an EL device which isdriven at a low voltage or current amount and which is superior ininterface stability between layers in the device and which has a highluminance as compared with the use of a conventional electrode.

As a result of intensive studies to solve the above-described problems,the present inventors have found that the above-described problems canbe solved, when orientation of a crystal constituting a conductive filmas an electrode for use, a size of the crystal, flatness of a filmsurface, and an atomic composition in the film are set to certainspecific values, and have completed the present invention.

That is, the present invention relates to the followings.

(1) An EL device comprising: a light emitting layer disposed as anessential layer between two electrodes facing each other, wherein atleast one of the electrodes includes a crystalline conductive film whosediffraction intensity ratio of (400)/(222) is 1.0 or more in X-raydiffraction by a θ/2θ process.

(2) The EL device according to (1), wherein the crystalline conductivefilm is an aggregate of columnar single crystals.

(3) The EL device according to (1) or (2), wherein the crystallineconductive film is a crystal aggregate in which a size of a crystallitein a longitudinal direction is in a range of 20 to 100 nm.

(4) The EL device according to one of (1) to (3), wherein a maximumsurface roughness of the crystalline conductive film is in a range of 5to 30 nm.

(5) The EL device according to one of (1) to (4), wherein an averagesurface roughness of a crystalline conductive film surface is in a rangeof 1 to 10 nm.

(6) The EL device according to one of (1) to (5), wherein the number of5 to 30 nm protrusions existing in a 1 μm square region in thecrystalline conductive film surface is 100 or more.

(7) An EL device comprising: a light emitting layer disposed as anessential layer between two electrodes facing each other, wherein thenumber of 5 to 30 nm protrusions existing in a 1 μm square region in thesurface of at least one of the electrodes is 100 or more.

(8) The EL device according to (7), wherein a maximum surface roughnessof at least one of the electrodes is in a range of 5 to 30 nm.

(9) The EL device according to (7) or (8), wherein an average surfaceroughness of at least one of the electrodes is in a range of 1 to 10 nm.

(10) The EL device according to one of (7) to (9), wherein at least oneof the electrodes is an aggregate of crystals having a (100) surfaceorientation.

(11) The EL device according to one of (7) to (10), wherein at least oneof the electrodes comprises a crystal aggregate in which a size of acrystallite in a longitudinal direction is in a range of 20 to 100 nm.

(12) The EL device according to one of (7) to (11), wherein at least oneof the electrodes is an aggregate of columnar single crystals.

(13) An EL device comprising: a light emitting layer disposed as anessential layer between two electrodes facing each other, wherein atleast one of the electrodes comprises a thin film of indium tin oxide,and tin atoms are uniformly distributed toward a film surface from asubstrate in the thin film.

(14) The EL device according to (13), wherein the indium tin oxide filmis a crystal aggregate having a (100) surface orientation.

(15) The EL device according to (13) or (14), wherein the thin film ofindium tin oxide is an aggregate of columnar single crystals.

(16) The EL device according to one of (13) to (15), wherein the thinfilm of indium tin oxide is a crystal aggregate in which a size of acrystallite in a longitudinal direction is in a range of 20 to 100 nm.

(17) The EL device according to one of (13) to (16), wherein a maximumsurface roughness of the thin film of indium tin oxide is in a range of5 to 30 nm.

(18) The EL device according to one of (13) to (17), wherein an averagesurface roughness of the thin film of indium tin oxide is in a range of1 to 10 nm.

(19) The EL device according to one of (12) to (18), wherein the numberof 5 to 30 nm protrusions existing in a 1 μm square region in thesurface of the thin film of indium tin oxide is 100 or more.

(20) An EL device comprising: a light emitting layer disposed as anessential layer between two electrodes facing each other, wherein atleast one of the electrodes is a conductive film manufactured on asubstrate by a spray thermal decomposition process or a pyro-solprocess.

(21) The EL device according to (20), wherein the conductive film isformed at a temperature on the substrate in a range of 400 to 750° C.

(22) The EL device according to (20) or (21), wherein the conductivefilm is a crystal aggregate having a (100) surface orientation.

(23) The EL device according to (20) to (22), wherein the conductivefilm is an aggregate of columnar single crystals.

(24) The EL device according to (20) to (23), wherein the conductivefilm is a crystal aggregate in which a size of a crystallite in alongitudinal direction is in a range of 20 to 100 nm.

(25) The EL device according to one of (20) to (22), wherein a maximumsurface roughness of the conductive film is in a range of 5 to 30 nm.

(26) The EL device according to one of (20) to (25), wherein an averagesurface roughness of the conductive film is in a range of 1 to 10 nm.

(27) The EL device according to one of (20) to (26), wherein the numberof 5 to 30 nm protrusions existing in a 1 μm square region in aconductive film surface is 100 or more.

(28) The EL device according to one of (1) to (27), wherein at least oneof the electrodes is a hole injection electrode.

(29) The EL device according to one of (1) to (28), wherein an organiccompound is used in the light emitting layer.

In the EL device of the present invention, the light emitting layer isdisposed as the essential layer between two electrodes facing eachother, and at least one of the electrodes includes the crystallineconductive film in which a diffraction intensity ratio of (400)/(222) is1.0 or more in the X-ray diffraction by the θ/2θ process.

In the electrode comprising the crystalline conductive film of thepresent invention, (400) may be detected as a main orientation surfacein the X-ray diffraction, and (222), (211), (411) or the like may alsobe detected as another orientation at a level smaller than that of themain orientation. When a main orientation ratio is represented by a(400)/(222) ratio in the X-ray diffraction intensity by the θ/2θprocess, the ratio is preferably 1.0 or more. When the ratio is lessthan 1.0, the driving voltage is high for the EL device of the presentinvention indicating 1.0 or more, and a luminance drops in the samedriving voltage. When the ratio is 1.0 or more, the diffractionintensity of the (222) surface is not especially limited, and may alsobe 0.

Moreover, in the EL device of the present invention, when a microfinestructure of the surface of the constituting electrode isconcave/convex, a charge or a hole injection efficiency advantageouslyincreases, and especially a uniformly distributed concave/convex surfaceis preferable. For example, when the protrusion number on the surface isused as in index for evaluating a surface concave/convex uniformity, thenumber of 5 to 30 nm protrusions existing in the 1 μm square region ispreferably 100 or more. In this case, the protrusion number means anaverage value of the number of 5 to 30 nm protrusions existing in the 1μm square region. It is to be noted that in this case, the protrusionindicates a clearly raised and recognized protrusion on an imageobtained in a case where the surface is measured using an interatomicforce microscope (AFC), scanning transmission microscope (STM), scanningelectron microscope (SEM) or the like. A length of the protrusion is avalue measured from a place having a lowest level in a trough of asectional curve of a surface roughness of the crystalline conductivefilm surface. When the number of protrusions is less than 100, a highvoltage is locally generated to cause luminance unevenness or the like.When the number is 100 or more, an upper limit of the number ofprotrusions is not especially limited. A shape of the protrusion is notespecially limited, but a protrusion top portion preferably has a shapewhich does not have an acute angle in consideration of contact with ahole transport layer or the like.

The electrode is preferably used especially as an anode, that is, a holeinjection electrode.

As a material for use in the anode, for example, a metal, alloy,electrically conductive compound or mixture having a large (4 eV ormore) work function is preferably usable, and concrete examples mayinclude metals such as Au. Moreover, the material usually has aconstitution in which an emitted light is taken out of a substrate sidein many cases, and therefore a transparent conductive material ispreferable. As this transparent conductive material, indium tin-dopedoxide (ITO), indium zinc-doped oxide (IZO), ZnO, SnO₂, In₂O₃, CuI or thelike is usable. They may be used as main components and, if necessary,one or two or more selected from a group consisting of oxide of Ir, Mo,Mn, Nb, Os, Re, Ru, Rh, Cr, Fe, Pt, Ti, W, and V may be contained in allthe metals in the film by 0.1 to 5 at %, for example, in terms ofmetals. If necessary, one or two or more selected from a groupconsisting of C, N, H, F, B, P, S, As, and Si elements may also becontained by 5 at % or less, for example, with respect to all metalatoms in the film.

A transmittance of the conductive film at the time when this material isused is 80% or more in a total transmittance, further preferably 80% ormore in a linear transmittance.

When ITO is used as the conductive material, usually In₂O₃ and SnO₂ arecontained in a stoichiometric composition, and an oxygen amount mayslightly deviate. When InO_(x).SnO_(y), X is preferably in a range of1.0 to 2.0, and Y is in a range of 1.6 to 2.4. A mixture ratio of SnO₂to In₂O₃ is in a range of preferably 0.05 to 40 wt %, more preferably 1to 20 wt %, further preferably 5 to 12 wt %.

When the electrode constituting the EL device of the present inventionis an ITO film, tin atoms in the film are uniformly distributed towardthe film surface from the substrate surface. Since tin does notsegregate on the surface of the film or in the film, the injectionefficiency of holes or electrons rises. In this case, uniformityindicates a state in which an indium/tin atom ratio is not inclined in adepth direction, and the indium/tin atom ratio in each depth is heldwithin an error range of 10% or less. In this case, for example, thefilm surface segregates, and a segregating portion is removed in asubsequent post-treatment process. Accordingly, the uniformed film isincluded in the present invention, when the indium/tin atom ratio iswithin an error range of 10% or less. However, when tin atoms isuniformly distributed toward the film surface from the substrate in thefilm immediately after film formation, a uniform film is more preferablyobtained without requiring any post-treatment process.

A method of manufacturing the electrode constituting the EL device ofthe present invention is not especially limited as long as the thin filmis formed on the substrate in the method, concrete examples may includea sputtering method, an electron beam method, an ion plating method or achemically vapor development method (CVD method), a spray thermaldecomposition method, a pyro-sol method, and the like, but especiallythe spray thermal decomposition method, or the pyro-sol method ispreferably usable.

More concretely, according to the sputtering method, a mixture of ametal (e.g., indium, zinc, etc.) and a doped metal (e.g., tin, fluorine,fluorine compound, aluminum, etc.) and oxygen gas, or metal oxides(e.g., indium oxide, zinc oxide, etc.) are sintered and used as atarget. By the electron beam method or the ion plating method, a mixtureof a metal (e.g., indium, zinc, etc.) and a doped metal (e.g., tin,fluorine, fluorine compound, aluminum, etc.) and oxygen gas, or metaloxides (e.g., indium oxide, zinc oxide, etc.) are sintered and used asan evaporated material. Accordingly, the transparent conductive film canbe formed.

When the conductive film comprising ITO is formed using the sputteringmethod, the film is preferably formed by a DC sputtering or RFsputtering method using a target of In₂O₃ doped with SnO₂. A projectedpower is in a range of preferably 0.1 to 10 W/cm², more preferably 0.1to 4 W/cm². Especially a power for a DC sputtering device is in a rangeof preferably 0.1 to 10 W/cm², especially preferably 0.2 to 7 W/cm². Afilm forming rate is in a range of preferably 2 to 100 nm/min,especially preferably 5 to 50 nm/min.

A sputtering gas is not especially limited, and an inactive gas of Ar,He, Ne, Kr, Xe or the like or a mixed gas may be used. These gases mayalso contain 20% or less of O₂. A pressure at a sputtering time of thesputtering gas may be usually about 0.1 to 20 Pa.

A substrate temperature at a film forming time is in a range ofpreferably 150 to 500° C., especially preferably 200 to 400° C. When thesubstrate temperature is low, crystal growth is not promoted at the filmforming time, and (100) orientation is not easily formed.

A heating treatment can be performed, if desired, after forming theconductive film such as ITO. A heating treatment temperature is in arange of preferably 100 to 550° C., more preferably 150 to 300° C., anda treatment time is preferably 0.1 to 3 hours, more preferably 0.3 to 1hour. A treatment atmosphere is preferably atmospheric air, nitrogen,oxygen, hydrogen added nitrogen atmosphere, organic solvent addedatmospheric air, nitrogen atmosphere or the like.

Moreover, in further detail, as an indium compound for use in the CVDmethod, spray thermal decomposition method, pyro-sol method or the like,a material thermally decomposed to form indium oxide is preferable.Concrete examples may include indium trisacetyl acetonate(In(CH₃COCHCOCH₃)₃), indium trisbenzoyl methanate (In(C₆H₅COCHCOC₆H₅)₃),indium trichloride (InCl₃), indium nitrate (In(NO₃)₃), indiumtriisopropoxide (In(OPr-i)₃) and the like. Above all, indium trisacetylacetonate is especially preferably usable.

Moreover, as a tin compound, a compound thermally decomposed to formstannic oxide is preferably usable. Concrete example may include stannicchloride, dimethyl tin dichloride, dibutyl tin dichloride, tetrabutyltin, stannous octoate (Sn(OCOC₇H₁₅)₂), dibutyl tin maleate, dibutyl tinacetate, dibutyl tin bisacetyl acetonate and the like.

It is to be noted that in addition to the indium compound and tincompound, as a third component, periodic table group II elements such asMg, Ca, Sr, and Ba, group III elements such as Sc, Y, lanthanoids suchas La, Ce, Nd, Sm, Gd, group IV elements such as Ti, Zr, Hf, group Velements such as V, Nb, Ta, group VI elements such as Cr, Mo, W, groupVII elements such as Mn, group IX elements such as Co, group X elementssuch as Ni, Pd, Pt, group XI elements such as Cu, Ag, group XII elementssuch as Zn, Cd, group XIII elements such as B, Al, Ga, group XIVelements such as Si, Ge, Pb, group XV elements such as P, As, Sb, groupXVI elements such as Se, Te and the like alone or a compound ispreferably added to form the ITO film.

An addition ratio of these elements is preferably 0.05 to 20 at % withrespect to indium, the addition ratio differs with an added element, andan element and addition amount may appropriately be selected inaccordance with a targeted resistance value.

As a method of forming the ITO film on a glass substrate by the pyro-solmethod or the spray thermal decomposition method, the film can bemanufactured by a method in which after dissolving the above-describedindium compound and tin compound into organic solvents of alcohols suchas methanol and ethanol, ketone such as acetone, methyl butyl ketone,and acetyl acetone or the like to constitute a mixed solution, the mixedsolution is formed into particulates and dispersed in a carrier gas, andbrought into contact with a glass substrate heated beforehand at 400 to750° C., preferably 400 to 550° C. under atmospheric pressure. The mixedsolution is formed into the particulates by an ultrasonic atomizationmethod, spraying method or the like. The ultrasonic atomization methodcapable of stably producing the particulates having uniform particulatediameters is preferable. An oxidizing gas, or usually air is used as acarrier gas.

When the pyro-sol method or the spray thermal decomposition method isused, a crystal nucleus having an ITO film composition is produced onthe glass substrate by the contact of the particulates of the mixedsolution with the glass substrate. When the nucleus grows, it contactsan adjacent nucleus, the contact nuclei are mutually bound, and growmainly in a vertical direction with respect to the substrate surface. Asa result, the ITO film which is a complex of oriented columnar singlecrystals is easily obtained.

As a substrate material, materials such as glass, quartz, resin,ceramic, and metal are preferably used. Above all, the glass substrateor a resin substrate is preferable which is inexpensive, easilyobtainable, and superior in physical aspects such as transmittance. Theglass substrate can be roughly classified into alkali glass andnon-alkali glass. The alkali glass is inexpensive and easily obtainable,and cost merits are large, but contains about 13 to 14% of alkali metaloxide. Therefore, there are defects that a countermeasure for preventingcontamination from these alkali metals is required, and heat resistanceis inferior. On the other hand, the non-alkali glass does not have anyfear that the alkali metal is contaminated, and has a certain degree ofheat resistance, but is comparatively expensive.

As the alkali glass, for example, soda lime glass or the like is knownhaving a composition of SiO₂: 72 wt %, Al₂O₃: 2 wt %, CaO: 8 wt %, MgO:4 wt %, Na₂O: 13.5 wt %. As the non-alkali glass, for example,borosilicate (7059) glass having a composition of SiO₂: 49 wt %,Al₂O₃:10 wt %, B₂O₃:15 wt %, and BaO: 25 wt %; borosilicate (AN) glasshaving a composition of SiO₂: 53 wt %, Al₂O₃:11 wt %, B₂O₃: 11 wt %,CaO: 2 wt %, MgO: 2 wt %, BaO: 15 wt %, ZnO: 6 wt %; borosilicate(NA-40) glass hg a composition of SiO₂: 54 wt %, Al₂O₃: 14 wt %, B₂O₃:15 wt %, MgO: 25 wt % or the like is known.

As the surface roughness of the substrate of glass or the like, theaverage surface roughness Ra≦10 nm, and the maximum surface roughnessRmax≦50 nm are preferable. Especially, in the substrate using alkaliglass, the average surface roughness Ra≦10 nm, and the maximum surfaceroughness Rmax≦50 nm are preferable. In the substrate using non-alkaliglass, the average surface roughness Ra≦5, and the maximum surfaceroughness Rmax≦20 nm are preferable. The lower limit value is notespecially regulated, and usually the average surface roughness isRa≧0.1 nm, and the maximum surface roughness is Rmax≧about 0.5 nm.

As a method of adjusting the surface roughness of the glass substrate inthe above-described range, mirror surface polishing may be performedusing diamond, cerium oxide or the like.

It is to be noted that with the use of alkali glass, to prevent thecontamination by the alkali metal components and the like from thesubstrate, after forming a barrier layer of SiO₂ or the like on thesubstrate, a conductive film of ITO or the like may be formed. Thebarrier layer can be formed by a vapor deposition method, sputteringmethod or the like, and the film thickness is preferably about 5 to 50nm. It is to be noted that when the barrier layer is formed, alkaliglass may have the average surface roughness Ra≦10 nm, and the maximumsurface roughness Rmax≦about 50 nm.

Concrete examples of a resin may include a film, sheet or plate formedof polyester such as polycarbonate, polyethylene terephthalate, andpolyarylate, polyether sulfonic resin, amorphous polyolefin,polystyrene, acryl resin or the like.

Especially from respects of transparency and moldability, a materialformed of a polyolefin-based transparent thermosetting resin ispreferable, and polyolefin-based copolymer obtained by polymerizing acomposite containing multifunctional monomer including two or moreunsaturated groups is more preferably used.

Concrete examples of the multifunctional monomer including two or moreunsaturated groups include: (i) di-, tri-, tetra-(meth)acrylates ofmultivalent alcohols, such as ethylene glycol di(meth)acrylate,diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,glycerol di(meth)acrylate, glycerol tri(meth)acrylate,trimethylolpropane di(meth)acrylate, trimethylolpropanetri(meth)acrylate, pentaerythritol di(meth)acrylate, and pentaerythritoltetra(meth)acrylate; (ii) aromatic multifunctional monomers such asp-divinyl benzene and o-divinyl benzene; (iii) esters such as(meth)acrylate vinyl ester, and (meth)acrylate aryl ester; (iv) dienessuch as butadiene, hexadiene, and pentadiene; (v) monomers having aphosphagen framework in which dichlorophosphagen is used as a rawmaterial and a polymer multifunctional group is introduced; (vi)multifunctional monomers having a hetero-atomic annular framework, suchas triaryl isocyanurate and the like.

From viewpoints of light resistance, resistance tooxidation/deterioration, and antistatic property, the transparentthermosetting resin preferably contains various ultraviolet absorbents,oxidation preventives, and charging preventives. When the transparentthermosetting resin is the polyolefin-based copolymer, thepolyolefin-based copolymer preferably uses a monomer having anultraviolet absorption property or an antioxidant property. Preferableexamples of the monomer include benzophenone-based ultraviolet absorbenthaving unsaturated double coupling, phenyl benzoate-based ultravioletabsorbent having the unsaturated double coupling, a (meth)acryalatemonomer including a hindered amino group as a substituent and the like.These monomers are preferably used in a range of 0.5 to 20 wt % withrespect to a total amount of monomers for use in obtaining a targetedpolyolefin-based copolymer.

In a surface state of the resin substrate for use, a root-mean-squarevalue of the surface roughness is 300 angstroms or less, and the numberof 600 angstroms or more protrusions existing in a 500 μm square regionon a flat surface is preferably 20 or less on the surface. It is to benoted that “the root-mean-square value of the surface roughness”mentioned with respect to the flat surface in the present invention is aroot-mean-square value of deviation from an average value of a height ofa concave/convex surface, and means a size of the concave/convex portionof the surface. Moreover, “the number of 600 angstroms or moreprotrusions existing in the 500 μm square region on the flat surface”mentioned in the present invention means the average value of the numberof protrusions having a height of 600 angstroms or more and existing ineach of ten 500 μm square regions optionally disposed on the flatsurface. The height and number of protrusions in each region can beobtained using an electron microscope, interatomic force microscope orthe like.

The substrate may also be obtained by any polymerization method andmolding method as long as the flat surface is disposed. The thickness isappropriately selectable in accordance with application or the like ofthe targeted organic EL device. When the transparent thermosetting resinsubstrate is formed of the polyolefin-based copolymer, the thickness ispreferably 0.1 to 1.5 mm, more preferably 0.1 to 1.0 mm in considerationof mechanical characteristics.

An inorganic oxide film provided with a gas barrier property may beformed on the substrate surface, if necessary, in order to preventoxygen, moisture, alkali component or the like from entering an organicsingle layer portion or an organic multilayered portion containingorganic emission materials described later. Concrete examples of theinorganic oxide film may include silicon oxide (SiO_(x)), aluminum oxide(Al₂O_(x)), titanium oxide (TiO_(x)), zirconium oxide (ZrO_(x)), yttriumoxide (Y₂O_(x)), ytterbium oxide (Yb₂O_(x)), magnesium oxide (MgO_(x)),tantalum oxide (Ta₂O_(x)), cerium oxide (CeO_(x)), or hafnium oxide(HfO_(x)), a polysilane film formed of an organic polysilane compound,an MgF₂ film, a CaF₂ film, and a film formed of composite oxide ofSiO_(x) and TiO_(x).

The film thickness of the inorganic oxide film is appropriatelychangeable by the material, but is generally in a range of 5 to 200 nm.When the film thickness is excessively thin, a desired gas barrierproperty cannot be imparted to the substrate. On the other hand, whenthe film thickness is excessively large, transmittance drops and, as aresult, a luminance of the organic EL device drops. The film thicknessof the inorganic oxide film is preferably 10 to 120 nm.

The flatness of the surface of the inorganic oxide film is preferably ashigh as that of a flat surface in the above-described substrate which isan underlayer of the inorganic oxide film in obtaining the organic ELdevice which does not have luminance unevenness and which has a highemission stability. The inorganic oxide film having such flatness can beformed by methods such as the sputtering method of a direct-currentsystem, magnetron system, high-frequency discharge system or the like, avacuum deposition method, an ion plating method, a plasma CVD method, adipping method, the spray thermal decomposition method, and the pyro-solmethod. Even when the inorganic oxide film is formed by any method, asubstrate temperature at the film forming time is preferably atemperature at which the substrate does not substantially cause thermaldeformation. When the resin substrate causes thermal deformation at thefilm forming time of the inorganic oxide film, it is difficult to obtainthe organic EL device that does not have any luminance unevenness andthat has the high emission stability.

Even when the conductive film formed on the substrate as described aboveis further irradiated with UV ozone, or ions such as an oxygen ion,nitrogen ion, and argon ion, the conductive film having theconcave/convex surface, which is a characteristic of the presentinvention, can be obtained. For example, conditions of the UV ozoneirradiation are that a main wavelength of a light source is 2537angstroms, 1849 angstroms, an oxygen gas introduction amount in anirradiation tank is 10 liters/minute, a substrate temperature is 10 to30° C., and an irradiation time is ten minutes to five hours. Theconditions of the ion irradiation include, for example, an innerpressure in the irradiation tank of 10⁻⁶ to 10⁻¹ Pa, an irradiationdriving voltage of 10 to 1000 V, and an irradiation time of ten secondsto one hour.

Moreover, the UV ozone irradiation and ion irradiation may also beperformed with respect to the conductive film having a desired surfaceconcave/convex state. When the UV ozone irradiation or the ionirradiation is performed, the conductive film surface can be cleanedwithout damaging the substrate.

The electrode constituting the EL device of the present invention havingthe above-described characteristics is preferably a crystallineconductive film. The film structure is not especially limited, and bulkcrystals may also be stacked in a structure, but above all, an aggregateof columnar single crystals is preferable. In this case, especially the(100) surface orientation becomes strong, and the EL device having a lowdriving voltage and high luminance can be manufactured.

In the crystalline conductive film, a size of a surface crystallitecontacting the light emitting layer, electron injection/transport layer,or hole injection/transport layer in a longitudinal direction, that is,a grain size is preferably in a range of 20 to 100 nm. When the size is100 nm or more, a local concave/convex state is enlarged. As a result, ahigh voltage is locally generated, luminance unevenness is caused, anddeterioration is accelerated to lower the emission stability. The localhigh voltage accelerates the crystallization of the organic compound inthe light emitting layer, and the luminance unevenness and emissionstability are lowered. When the size is 20 nm or less, the crystal doesnot sufficiently grow into a (100) surface direction, the electron orhole cannot be efficiently transported into the light emitting layer orthe like at a low voltage, and emission efficiency drops.

The shape of the crystallite is not especially limited, but a sphericalshape or a rotary elliptic shape is preferable, and there are preferablyless protrusions or corners. It is to be noted that the shape and sizeof the crystallite can be evaluated by observation of the surface usinga transmission microscope (TEM).

Moreover, in the crystalline conductive film of the present invention,the maximum surface roughness (Rmax) of the surface contacting the lightemitting layer, electron injection/transport layer, or holeinjection/transport layer is in a range of preferably 5 to 30 nm, morepreferably 5 to 20 nm in the film. In the contact surface, theprotrusion or roughness of the electrode surface has heretofore beensuppressed, and it has been effective to flatten the surface as much aspossible in order to prevent emission defects by a leak current,generation of a dark spot, and deterioration of the device with anelapse of time. However, when there is a concave/convex in the structureof a microfine surface, a surface area increases, and the injectionefficiency of the electron or hole rises. Therefore, when Rmax is 5 nmor less, the surface is too flat, and the injection efficiency of theelectron or hole drops. When the roughness is 30 nm or more, the localconcave/convex is enlarged. As a result, a high voltage is locallygenerated, luminance unevenness is caused, and the deterioration isaccelerated to lower the emission stability. In the above description,from another viewpoint, the average film surface roughness (Ra) ispreferably in a range of 1 to 10 nm. When Ra is less than 1 nm, thesurface is excessively flat, and the injection efficiency of theelectron or hole drops. When the roughness is larger than 10 nm, thelocal concave/convex is enlarged. As a result, the high voltage islocally generated, the luminance unevenness is caused, and thedeterioration is accelerated to lower the emission stability.

As described above, the thickness of the conductive film for use in theelectrode may be a certain or more thickness by which the hole orelectron can be sufficiently injected, and is in a range of preferably10 to 500 nm, further preferably 20 to 200 nm. Moreover, an upper limitis not especially limited. However, when the film is excessively thick,a fear of peeling or the like occurs. When the film is excessively thin,there is a problem in film strength or a hole transport capability at amanufacturing time.

The EL device manufactured in the present invention includes the holeinjection electrode on the substrate, and further the electron injectionelectrode. At least a charge transport layer and a light emitting layerare disposed between these electrodes, and a protective electrode isfurther disposed as an uppermost layer. It is to be noted that thecharge transport layer may be omitted. Moreover, the electron injectionelectrode comprises a metal, compound, or alloy formed by vapordeposition, sputtering, or the like, preferably the sputtering andhaving a small work function, and the hole injection electrode comprisesthe above-described constitution.

As the constituting material of the electron injection electrode formedin the film, a material which effectively injects the electrons andwhich has a low work function is preferable. For example, simple metalelements such as K, Li, Na, Mg, La, Ce, Ca, Sr, Ba, Al, Ag, In, Sn, Zn,Zr, Cs, Er, Eu, Ga, Hf, Nd, Rb, Sc, Sm, Ta, Y, and Yb, or compounds suchas BaO, BaS, CaO, HfC, LaB₆, MgO, MoC, NbC, PbS, SrO, TaC, ThC, Tho₂,ThS, TiC, TiN, UC, UN, UO₂, W₂C, Y₂O₃, ZrC, ZrN, and ZrO₂ may be used.Two-component, three-component alloy containing the metal elements ispreferably used in order to enhance the stability. As an alloy base, forexample, aluminum-based alloys such as Al.Ca (Ca: 0.01 to 20 at %,especially 5 to 20 at %), Al.In (In: 1 to 10 at %), and Al.Li (Li: 0.01to 14 at %, especially 0.3 or more and less than 14 at %), In.Mg (Mg: 50to 80 at %) and the like are preferable. Above all, especially a simpleAl material, and aluminum-based alloys such as Al.Li (Li: 0.4 to 6.5(additionally, 6.5 is not included) at %) or (Li: 6.5 to 14 at %) arepreferable because a compressive stress is not easily generated.Therefore, as a sputtering target, the electron injection electrodeconstituting metal or alloy is usually used. The work function is 4.5 eVor less, and the metal or alloy having a work function of 4.0 eV or lessis especially preferable.

When the sputtering method is used in forming the film of the electroninjection electrode, in the formed electron injection electrode film,sputtered electron or electron group has a comparatively high movementenergy as compared with the vapor deposition. Therefore, a surfacemigration effect works, and adhesion in an organic layer interface isenhanced. Moreover, when pre-sputtering is performed, a surface oxidelayer is removed in vacuum, moisture or oxygen adsorbed by an organiclayer interface can be removed by reverse sputtering, and therefore aclean electrode-organic layer interface or electrode can be formed. As aresult, a high-level stable organic EL device can be obtained. As atarget, an alloy or a metal alone in the composition range may also beused. Additionally, a target of an added component may also be used.Furthermore, even when a mixture of materials having largely differentsteam pressures is used as the target, there is little deviation of thecomposition between the film to be produced and the target, and thematerial for use is not limited by the steam pressure as in the vapordeposition method. It is not necessary to supply the material for a longtime as compared with the vapor deposition, uniformity in film thicknessor film quality is superior, and productivity is advantageous.

The electron injection electrode formed by the sputtering method is adense film, and therefore an organic EL device is obtained in which verylittle moisture enters the film as compared with a coarse deposited filmand which has a high chemical stability and a long life.

A pressure of a sputtering gas at a sputtering time is in a range ofpreferably 0.1 to 5 Pa. When the pressure of the sputtering gas isadjusted in this range, an Al.Li alloy having an Li concentration in theabove-described range can be easily obtained. When the pressure of thesputtering gas is changed in the range during the film formation, theelectron injection electrode having the Li concentration gradient can beeasily obtained.

As the sputtering gas, an inactive gas for use in a usual sputteringdevice is usable. In reactive sputtering, instead, reactive gases suchas N₂, H₂, O₂, C₂H₄, and NH₃ are usable.

A high-frequency sputtering method or the like using an RF power supplyis also possible as the sputtering method, but the DC sputtering methodis preferably used, because a film forming rate is easily controlled anda damage onto an organic EL device structural body is reduced. A powerof the DC sputtering device is in a range of preferably 0.1 to 10 W/cm²,especially 0.5 to 7 W/cm². The film forming rate is in a range ofpreferably 5 to 100 nm/min, especially 10 to 50 nm/min.

The thickness of the electron injection electrode thin film may be notless than a certain thickness with which the electron is sufficientlyinjected, and may be 0.1 nm or more, preferably 1 nm or more, morepreferably 3 nm or more. The upper limit value is not especiallylimited, and usually the film thickness is 1 to 500 nm, preferably about3 to 500 nm.

In the organic EL device of the present invention, a protectiveelectrode may also be disposed on the electron injection electrode, thatis, on the side opposite to the organic layer. When the protectiveelectrode is disposed, the electron injection electrode is protectedfrom outside air, moisture or the like, the constituting thin film isprevented from being deteriorated, the electron injection efficiency isstabilized, and the device life is rapidly enhanced. Moreover, thisprotective electrode has a very low resistance. When the resistance ofthe electron injection electrode is high, the electrode also has afunction of a wiring electrode. This protective electrode contains anyone or two or more of Al, Al and transition metal (additionallyexcluding Ti), Ti or titanium nitride (TiN). When they are used alone,the protective electrode preferably contains at least Al: 90 to 100 at%, Ti: 90 to 100 at %, TiN: 90 to 100 mol %. Moreover, when two or moreare used, a mixture ratio is optional, but in a mixture of Al and Ti, acontent of Ti is preferably 10 at % or less. A layer containing themalone may also be stacked. Especially, when Al, Al and transition metalare used as a wiring electrode described later, a satisfactory effect isobtained, TiN has a high resistance to corrosion, and an effect of asealing film is large. TiN may also deviate from a stoichiometricalcomposition by about 10%. Furthermore, the alloy of Al and transitionmetal may especially preferably contain transition metals such as Mg,Sc, Nb, Zr, Hf, Nd, Ta, Cu, Si, Cr, Mo, Mn, Ni, Pd, Pt, W by 10 at % orless, especially 5 at % or less, especially 2 at % or less. With a lesscontent of the transition metal, a thin film resistance is lowered in acase where the metal functions as a wiring material.

To secure the electron injection efficiency or to prevent penetration ofmoisture, oxygen, or organic solvent, the thickness of the protectiveelectrode may be not less than a certain thickness, and is in a range ofpreferably 50 nm or more, further preferably 100 nm or more, especiallypreferably 100 to 1000 nm. When the protective electrode layer isexcessively thin, the above-described effect is not obtained, a stepcoating property of the protective electrode layer drops, and connectionwith a terminal electrode is not sufficient. On the other hand, when theprotective electrode layer is excessively thick, the stress of theprotective electrode layer is large, and therefore a growth rate of adark spot is high. It is to be noted that the film thickness of theelectron injection electrode is small, and therefore a film resistanceis high. To compensate for this, the thickness is usually about 100 to500 nm in a case where the electrode functions as the wiring electrode,and about 100 to 300 nm in a case where the electrode functions asanother wiring electrode.

The total thickness of the electron injection electrode and protectiveelectrode is not especially limited, but may be usually about 100 to1000 nm.

A constitution example of an organic EL light emitting devicemanufactured by the present invention is shown in FIG. 1. The EL deviceshown in FIG. 1 successively includes a hole injection electrode 2, holeinjection/transport layer 3, light emitting and electroninjection/transport layer 4, electron injection electrode 5, andprotective electrode 6 on the substrate 1.

The organic EL device of the present invention is not limited to a shownexample, and can be various constitutions. For example, the lightemitting layer is disposed alone, and the electron injection/transportlayer may also be interposed between the light emitting layer and theelectron injection electrode in the structure. Moreover, if necessary,the hole injection/transport layer and the light emitting layer may alsobe mixed.

The hole injection electrode and electron injection electrode can beformed as described above, and organic layers such as the light emittinglayer may be formed by vacuum evaporation or the like, but these filmscan be patterned by methods such as etching, if necessary, after maskevaporation or film formation, and a desired light emitting pattern canbe obtained. Furthermore, a thin film transistor (TFT) is formed on thesubstrate, each film is formed in accordance with the pattern, and adisplaying and driving pattern may also be formed as such.

After the film of the electrode is formed, in addition to the protectiveelectrode, a protective film may also be formed using inorganicmaterials such as SiO_(x), organic materials such as Teflon andchlorine-containing fluoride carbon polymer or the like. The protectivefilm may be transparent or opaque, and the protective film has athickness of about 50 to 1200 nm. The protective film may be formed by ageneral sputtering method, vapor deposition method or the like inaddition to the reactive sputtering method.

Furthermore, a sealing layer is preferably formed on the device in orderto prevent the organic layer or the electrode of the device from beingoxidized. In the sealing layer, adhesive resin layers such as acommercially available low-absorption photo-setting adhesive forpreventing penetration of humidity, silicone-based adhesive, andadhesive resin layers such as a bridged ethylene-vinyl acetate copolymeradhesive sheet are used, and sealing plates such as a glass plate arebonded and sealed. A metal plate, plastic plate and the like may also beused in addition to the glass plate.

Next, an organic layer disposed on the EL device of the presentinvention will be described. The light emitting layer has an injectionfunction of the hole (positive hole) and electron, transport function,and a function of producing an exciton by recombination of the hole andelectron. A comparatively electronically neutral compound is preferablyused in the light emitting layer.

The hole injection/transport layer has a function of facilitating theinjection of the hole from the hole injection electrode, a function oftransporting the hole steadily, and a function of hindering theelectron, and the electron injection/transport layer has a function offacilitating the injection of the electron from the electron injectionelectrode, a function of transporting the electron steadily, and afunction of hindering the hole. These layers increase/seal the hole orelectron injected in the light emitting layer, optimizes a recombinedregion, and improves a light emitting efficiency.

The thickness of the light emitting layer, the thickness of the holeinjection/transport layer, and the thickness of the electroninjection/transport layer are not especially limited, but differ with aforming method, and are usually preferably about 5 to 500 nm, especially10 to 300 nm.

The thickness of the hole injection/transport layer or the electroninjection/transport layer may be set to be approximately equal to orabout 1/10 to ten times the thickness of the light emitting layerdepending on the design of a recoupling/light emitting region. When eachinjection layer for the hole or electron is separated from the transportlayer, the thickness of the injection layer is preferably 1 nm or more,and the transport layer is 1 nm or more. An upper limit of the thicknessof the injection layer or the transport layer at this time, is usuallyabout 500 nm in the injection layer, about 500 nm in the transportlayer. This film thickness also applies to a case where twoinjection/transport layers are disposed.

The light emitting layer of the organic EL device of the presentinvention contains a fluorescent substance which is a compound having alight emitting function. Examples of the fluorescent substance include acompound described in Japanese Patent Application Laid-Open No.63-264692, and at least one selected from compounds such asquinacridone, rubrene, and styryl-based dyestuffs. Further examplesinclude quinoline derivatives such as a metal complex dyestuff in which8-quinolinol such as tris(8-quinolinolate)aluminum and derivative areused as ligand, tetraphenyl butadiene, anthracene, perylene, coronene,12-phthalo perinone derivative and the like.

Moreover, combined use with a host substance capable of emitting lightby itself is preferable, and used as a dopant is preferable. In thiscase, a content of the compound in the light emitting layer is 0.01 to10 wt %. further preferably 0.1 to 5 wt %. By the combined use with thehost substance, a light emitting wavelength characteristic of the hostsubstance can be changed, emission is possible in which the wavelengthshifts to a long wavelength, and the light emitting efficiency or thestability of the device is enhanced.

As the host substance, a quinolinolate complex is preferable, andfurther an aluminum complex is preferable using 8-quinolinol orderivative as the ligand. Examples include aluminum complexes describedin Japanese Patent Application Laid-Open Nos. 63-264692, 3-255190,5-70733, 5-258859, 6-215874 and the like.

Concrete examples first include tris(8-quinolinolate)aluminum,bis(8-quinolinolate)magnesium, bis(benzo{f}-8-quinolinolate) zinc,bis(2-methyl-8-quinolinolate)aluminum oxide, tris(8-quinolinolate)indium, tris(5-methyl-8-quinolinolate)aluminum, 8-quinolinolate lithium,tris(5-chloro-8-quinolinolate)gallium,bis(5-chloro-8-quinolinolate)calcium, 5,7-dichloro-8-quinolinolatealuminum, tris(5,7-dipromo-8-hydroxyquinolinolate)aluminum,poly[zinc(II)-bis(8-hydroxy-5-quinolinyl)methane] and the like.

Moreover, the substance may also be an aluminum complex including theligand opposite to 8-quinolinol and the derivative, and examples includebis(2-methyl-8-quinolinolate) (phenolate)aluminum(III),bis(2-methyl-8-quinolinolate) (ortho-cresolate)aluminum(III),bis(2-methyl-8-quinolinolate) (metha-cresolate)aluminum(III),bis(2-methyl-8-quinolinolate) (para-cresolate)aluminum(III),bis(2-methyl-8-quinolinolate) (ortho-phenylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate) (metha-phenylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate) (para-phenylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate) (2,3-dimethylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate) (2,6-dimethylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate) (3,4-dimethylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate) (3,5-dimethylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate) (3,5-di-tert-butylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate)(2,6-diphenylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate) (2,4,6-triphenylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate) (2,3,6-trimethylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate)(2,3,5,6-tetramethylphenolate)aluminum(III),bis(2-methyl-8-quinolinolate) (1-naphtholate)aluminum(III),bis(2-methyl-8-quinolinolate) (3-naphtholate)aluminum(III),bis(2,4-dimethyl-8-quinolinolate) (ortho-phenylphenolate)aluminum(III),bis(2,4-dimethyl-8-quinolinolate) (para-phenylphenolate)aluminum(III),bis(2,4-dimethyl-8-quinolinolate) (metha-phenylphenolate)aluminum(III),bis(2,4-dimethyl-8-quinolinolate) (3,5-dimethylphenolate)aluminum(III),bis(2,4-dimethyl-8-quinolinolate)(3,5-di-tert-butylphenolate)aluminum(III),bis(2-methyl-4-ethyl-8-quinolinolate) (para-cresolate)aluminum(III),bis(2-methyl-4-methoxy-8-quinolinolate)(para-phenylphenolate)aluminum(III),bis(2-methyl-5-cyano-8-quinolinolate) (ortho-cresolate)aluminum(III),bis(2-methyl-6-trifluoromethyl-8-quinolinolate)(2-naphtholate)aluminum(III) and the like.

Additionally, the examples may include bis(2-methyl-8-quinolinolate)aluminum(III)-μ-oxo-bis(2-methyl-8-quinolinolate)aluminum(III),bis(2,4-dimethyl-8-quinolinolate)aluminum(III)-μ-oxo-bis(2,4-dimethyl-8-quinolinolate)aluminum(III),bis(4-ethyl-2-methyl-8-quinolinolate)aluminum(III)-μ-oxo-bis(4-ethyl-2-methyl-8-quinolinolate)aluminum(III),bis(2-methyl-4-methoxyquinolinolate)aluminum(III)-μ-oxo-bis(2-methyl-4-methoxyquinolinolate)aluminum(III),bis(5-cyano-2-methyl-8-quinolinolate)aluminum(III)-μ-oxo-bis(5-cyano-2-methyl-8-quinolinolate)aluminum(III),bis(2-methyl-5-trifluoromethyl-8-quinolinolate)aluminum(III)-μ-oxo-bis(2-methyl-5-trifluoromethyl-8-quinolinolate)aluminum(III)and the like.

As another host substance, a phenyl anthracene derivative described inJapanese Patent Application Laid-Open No. 8-12600, a tetraarylethenederivative described in Japanese Patent Application Laid-Open No.8-12969, and the like are also preferable.

The light emitting layer may also serve as the electroninjection/transport layer, and in this casetris(8-quinolinolate)aluminum or the like is preferably used. Thesefluorescent substance may be vapor-deposited.

Moreover, if necessary, the light emitting layer is also preferably amixed layer of at least one or more types of hole injection/transportcompounds and at least one or more types of electron injection/transportcompounds, and the mixed layer preferably contains a dopant. A contentof the compound in this mixed layer is preferably 0.01 to 20 wt %,further preferably 0.1 to 15 wt %.

In the mixed layer, since a hopping conduction path of a carrier isformed, each carrier moves in a dominant polar substance, carrierinjection of a reverse polarity does not easily occur, an organiccompound is not easily damaged, and there is another advantage that thedevice life lengthens. However, when the mixed layer contains thedopant, emission wavelength characteristics of the mixed layer itselfcan be changed, and the emission wavelength can be shifted to the longwavelength. Moreover, an emission intensity can be increased, andstability of the device can be enhanced.

The hole injection/transport compound and electron injection/transportcompound for use in the mixed layer may be selected from the compoundsfor the hole and electron injection/transport layers described later.Above all, as the compound for the hole injection/transport layer, it isalso preferable to use an amine derivative having intense fluorescence,for example, a triphenyl diamine derivative which is the hole transportmaterial, further a styryl amine derivative, and an amine derivativehaving an aromatic condensed ring.

As the electron injection/transport compound, a quinoline derivative,further a metal complex including 8-quinolinol or the derivative asligand, especially tris(8-quinolinolate)aluminum (Alq3) are preferablyused. Moreover, the above-described phenyl anthracene derivative, andtetraarylethene derivative are also preferably used.

In this case, a mixture ratio is determined in consideration of carriermobility and carrier concentration, but in general, a weight ratio ofthe compound having the compound/electron injection/transport functionin the hole injection/transport compound is preferably 1/99 to 99/1,further preferably 10/90 to 90/10, especially preferably about 20/80 to80/20.

Moreover, the thickness of the mixed layer preferably ranges from athickness corresponding to a molecular layer to be less than the filmthickness of the organic compound layer, and is concretely preferably 1to 85 nm, further preferably 5 to 60 nm, especially preferably 5 to 50nm.

Moreover, as a method of forming the mixed layer, co-evaporation forevaporation from different evaporation sources is preferable. However,when a steam pressure (evaporation temperature) is substantially equalor very close, the layers may also be mixed in the same evaporationboard, and evaporated. In the mixed layer, the compounds are preferablyuniformly mixed. However, as the case may be, the compounds may exist ininsular forms. In the light emitting layer, in general, an organicfluorescent substance is evaporated, or is dispersed in a resin binderto coat the layer, and accordingly the light emitting layer is formed ina predetermined thickness.

Moreover, in the hole injection/transport layer, for example, variousorganic compounds described in Japanese Patent Application Laid-OpenNos. 63-295695, 2-191694, 3-792, 5-234681, 5-239455, 5-299174, 7-126225,7-126226, 8-100172, EP-650955A1 and the like are usable. The examplesinclude a tetra aryl benzidine compound (triaryl diamine or triphenyldiamine: TPD), aromatic class 3 amine, hydrazone derivative, carbazolederivative, triazole derivative, imidazole derivative, oxadiazolederivative having an amino group, polythiophen and the like. Two or moretypes of these compounds may also be used, the compounds for combineduse may be stacked in separate layers, and mixed.

When the hole injection/transport layer is divided and stacked in thehole injection layer and hole transport layer, a preferable combinationcan be selectively used from the compounds for the holeinjection/transport layer. At this time, the layers are preferablystacked in order from a compound having a small ionization potentialfrom a hole injection electrode (ITO, etc.) side. A compound having asatisfactory thin film property is preferably used on a hole injectionelectrode surface. This stacking order also applies to a case where twoor more hole injection/transport layers are disposed. By this stackingorder, a driving voltage drops, and the generation of a current leak orgeneration/growth of a dark spot can be prevented. When the device isformed, evaporation is used. Therefore, an about 1 to 10 nm thin filmcan be uniform and pinhole free. Even with the use of a compound havinga small ionization potential and having absorption in a visible portionin the hole injection layer, the efficiency can be prevented fromdropping because of color change of emitted color or re-absorption. Thehole injection/transport layer can be formed by evaporation of theabove-described compound in the same manner as in the light emittinglayer.

Moreover, in the electron injection/transport layer disposed ifnecessary, quinoline derivatives such as the organic metal complex using8-quinolinol such as tris(8-quinolinolate)aluminum (Alq3) or thederivative as ligand, oxadiazole derivative, beryline derivative,pyridine derivative, pyrimidine derivative, quinoxaline derivative,diphenylquinone derivative, nitro substituent fluorine derivative andthe like are usable. In this case, tris(8-quinolinolate)aluminum or thelike is preferably used. The electron injection/transport layer may beformed by vapor deposition or the like in the same manner as in thelight emitting layer.

When the electron injection/transport layer is divided and stacked inthe electron injection layer and electron transport layer, a preferablecombination can be selectively used from the compounds for the electroninjection/transport layer. At this time, the layers are preferablystacked in order from a compound having a large electron affinity valuefrom an electron injection electrode side. This stacking order alsoapplies to a case where two or more electron injection/transport layersare disposed.

The emitted color may be controlled using a color change film indicatinga color filter film or a fluorescent substance in the substrate, or aderivative reflective surface.

A color filter for use in a liquid crystal display or the like may beused in the color filter film, but the characteristics of the colorfilter may be adjusted in accordance with the color emitted by organicEL to optimize taking efficiency/color purity.

Moreover, by the use of a color filter capable of cutting outside lighthaving a short wavelength optically absorbed by EL device materials orfluorescent conversion layer, light resistance of the device or contrastof the display is also enhanced.

Moreover, optical thin films such as a derivative multilayered film mayalso be used instead of the color filter.

The fluorescent conversion filter film absorbs EL emitted light, anddischarge the light from a fluorescent body in the fluorescentconversion film to change the emitted color, and the composition isformed by three: a binder; a fluorescent material; and aphoto-absorption material.

A fluorescent material basically having a high fluorescent quantum yieldmay be used, and absorption is preferably intense in an EL emittedwavelength region. In actual, a laser dyestuff or the like is suitable,and rhodamine-based compound, beryline-based compound, cyanine-basedcompound, phthalocyanine-based compound (also including sub-phthaloetc.), naphthaloimide-based compound, condensed ring hydrocarbon-basedcompound, condensed complex ring-based compound, styryl-based compound,coumarine-based compound and the like are usable.

A material which does not basically extinguish fluorescence may beselected as a binder, and a material capable of performing microfinepatterning is preferable in photolithography, printing or the like. Amaterial which is not damaged at the film forming time of ITO ispreferable.

An optical absorption material is used, when optical absorption of thefluorescent material is insufficient, but may not be used, if notnecessary. An optical absorption material which does not extinguish thefluorescence of the fluorescent material may be selected.

A vacuum evaporation method is preferably used, because homogeneous thinfilms can be formed in forming the hole injection/transport layer, lightemitting layer, and electron injection/transport layer. When the vacuumevaporation method is used, a homogeneous thin film having an amorphousstate or a crystal particle diameter of 0.1 μm or less is obtained. Whenthe crystal particle diameter exceeds 0.1 μm, nonuniform emissionresults, the driving voltage of the device has to be raised, andinjection efficiency of charges remarkably drops.

The conditions of the vacuum evaporation are not especially limited, buta vacuum degree of 10⁻⁴ Pa or less is set, and an evaporation rate ispreferably set to about 0.01 to 1 nm/sec. The respective layers arepreferably formed continuously in vacuum. When the layers arecontinuously formed in vacuum, impurities can be inhibited from beingadsorbed in the interface between the layers, and therefore highcharacteristics are obtained. The driving voltage of the device can belowered, and the dark spot can be inhibited from growing/beinggenerated.

When the vacuum evaporation method is used in forming the respectivelayers, and when one layer contains a plurality of compounds, ports viawhich the compounds are injected are preferably controlled attemperature and co-evaporated.

The organic EL device of the present invention may also be driven by adirect current, pulse, or alternating current. An applied voltage isusually set to about 2 to 30 V.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a constitution example of anorganic EL device.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described hereinafter in accordance withexamples in further detail, but the scope of the present invention isnot limited to the examples.

EXAMPLE 1

An ITO film was prepared on a glass substrate by a pyro-sol method. Thatis, an alkali glass substrate (250×250×1 mm) pre-coated with an SiO₂film (film thickness of 150 nm) was projected into a conveyor furnaceheated at 500° C. by a belt conveyor, an acetyl acetone solution ofstannic chloride-indium acetyl acetone containing 5% by atom of tinatoms was formed in fog drips. Air was used as a carrier gas, blown intothe conveyor furnace, brought into contact with the surface of a glasssubstrate, and thermally decomposed to form the ITO film. A surfaceresistance value of the obtained ITO film was 25 Ω/□ and a filmthickness was 100 nm. In observation of the film surface by AFM, 100 ormore 5 nm to 30 nm protrusions were observed in a 1 μm square, anaverage surface roughness (Ra) was 1.5 nm, and a maximum surfaceroughness (Rmax) was 18 nm. As a result of X-ray diffraction, the filmwas preferentially oriented in a (400) surface, and an X-ray intensityratio of (400)/(222) was 5.82.

Moreover, when a composition of metal atoms in the film was measuredusing ESCA, an indium/tin atomic ratio was a certain ratio in a depth ofa substrate direction from the surface, and atoms existed within anerror range of 10% or less.

An EL device was prepared using glass provided with the ITO filmadjusted as described above. On the ITO film which was cleaned and fromwhose surface organic materials were removed, a vacuum evaporationmethod was used, a hole transport layer of N,N′-diphenyl-N,N′-di(m-tryl)benzidine (abbreviation: TPD) having a film thickness of 30 nm, a lightemitting layer of an aluminoquinolinol complex (abbreviation: Alq3)having a thickness of 50 um, and finally a counter electrode of an Ag—Mgalloy (weight ratio Ag/Mg=1/10) having a thickness of 200 nm weresuccessively stacked to prepare an organic EL device.

A direct-current voltage was applied to the organic EL device preparedas described above every 0.5 V to check a relation of a voltage(V)-current density (mA/cm²)-emission luminance (cd/cm²). As a result, acurrent density for emission of 100 cd/cm² was 3.7 mA/cm², and a voltagewas 4.3 V. Moreover, a maximum emission luminance was 16300 cd/cm² atthe time of application of 11.5 V.

COMPARATIVE EXAMPLE 1

An ITO film was prepared on a glass substrate by a sputtering method.That is, an alkali glass substrate (250×250×1 mm) pre-coated with anSiO₂ film (film thickness of 150 nm) was set in a film forming chamber,and a pressure was reduced to 1.3×10⁻³ Pa. ITO (In₂O₃ containing 10 wt %of SnO₂) was used as a target, Ar+O² (flow rate=100:1) was used as asputtering gas, and an ITO thin film was formed in a thickness of 100 nmat a pressure of 3.1×10⁻¹ Pa at the time of the sputtering and in a DCsputtering power of 1.7 kW. A substrate temperature at a film formingtime was 300° C. When a composition of the obtained ITO thin film waschecked, In₂O₃: 90.2 wt %, SnO₂: 9.8 wt %. As a result of X-raydiffraction of the ITO thin film obtained without performing any heatingtreatment, the film was preferentially oriented in a (222) surface, andan X-ray intensity ratio of (400)/(222) was 0.69. A surface resistancevalue was 17 Ω/□. In observation by AFM, 70 to 80 5 to 30 nm protrusionswere observed in a 1 μm square, an average surface roughness (Ra) was9.4 nm, and a maximum surface roughness (Rmax) was 72 nm.

Moreover, when a composition of metal atoms in the film was measuredusing ESCA, a tin atomic ratio was 20% on the surface, and segregationof tin atoms was observed in the surface.

An EL device was prepared using glass provided with the ITO filmadjusted as described above in the same manner as in Example 1.

A direct-current voltage was applied to the organic EL device preparedas described above every 0.5 V to check a relation of a voltage(V)-current density (mA/cm²)-emission luminance (cd/cm²). As a result, acurrent density for emission of 100 cd/cm² was 4.6 mA/cm², and a voltagewas 4.2 V. Moreover, a maximum emission luminance was 14000 cd/cm² atthe time of application of 9 V.

In comparison of Example 1 with Comparative Example 1, the currentdensity for the emission with luminance of 100 cd/cm² of Example 1 waslower, and it can be said that emission is possible at a low currentdensity. This means that the device can be driven at a lower voltage ina case where a film having an equal surface resistance is used. Themaximum emission luminance of Example 1 is higher in the equal drivingvoltage. When the above description is put together, it can be said thatthe EL device of the present invention has emission characteristics witha lower voltage and a higher luminance as compared with a conventionaldevice.

INDUSTRIAL APPLICABILITY

As described above, by use of an electrode including a conductive filmof the present invention, the electrode is driven with a lower voltageor current amount as compared with a conventional electrode. Since ahigher-luminance emission is achieved at an applied voltage having anequal voltage or current amount, an EL device indicating a less powerconsumption and having a longer life can be manufactured, and anindustrial use value can be said to be high.

1. An EL device comprising: a light emitting layer disposed as an essential layer between two electrodes facing each other, wherein at least one of the electrodes includes a crystalline conductive film surface whose diffraction intensity ratio of (400)/(222) is 1.0 or more in X-ray diffraction by a θ/2θ process, wherein the crystalline conductive film is a crystal aggregate in which a size of a crystallite in a longitudinal direction is in a range of 20 to 100 nm, wherein an organic compound is used in the light emitting layer.
 2. The EL device according to claim 1, wherein the crystalline conductive film is an aggregate of columnar single crystals.
 3. The EL device according to claim 1, wherein a maximum surface roughness of the crystalline conductive film is in a range of 5 to 30 nm.
 4. The EL device according to claim 1, wherein an average surface roughness of a crystalline conductive film surface is in a range of 1 to 10 nm.
 5. The EL device according to claim 1, wherein a number of 5 to 30 nm protrusions existing in a 1 μm square region in the crystalline conductive film surface is 100 or more.
 6. The EL device according to claim 1, wherein at least one of the electrodes is a hole injection electrode.
 7. An EL device comprising: a light emiffing layer disposed as an essential layer between two electrodes facing each other, wherein a number of 5 to 30 nm protrusions existing in a 1 μm square region in a surface of at least one of the electrodes is 100 or more and wherein an organic compound is used in the light emitting layer.
 8. The EL device according to claim 7, wherein a maximum surface roughness of at least one of the electrodes is in a range of 5 to 30 nm.
 9. The EL device according to claim 7, wherein an average surface roughness of at least one of the electrodes is in a range of 1 to 10 nm.
 10. The EL device according to claim 7, wherein at least one of the electrodes is an aggregate of crystals having a (100) surface orientation.
 11. The EL device according to claim 7, wherein at least one of the electrodes comprises a crystal aggregate in which a size of a crystallite in a longitudinal direction is in a range of 20 to 100 nm.
 12. The EL device according to claim 7, wherein at least one of the electrodes is an aggregate of columnar single crystals.
 13. The EL device according to claim 7, wherein at least one of the electrodes is a hole injection electrode. 